The invention relates to an actuating device for selecting gear steps of a shift-by-wire gearshift transmission, with a mechanical transmission means for parking lock actuation, according to the preamble of claim 1.
Parking locks are always employed when non-mechanical components are used for transmitting drive forces in an automobile, in particular in automatic transmissions having a hydrodynamic torque converter, i.e., if no continuous positive mechanical connection exists between the automobile engine and the wheels of the automobile even if a gear is engaged.
Automobiles with automatic transmission therefore have typically a parking lock to prevent the vehicle from accidentally rolling when the vehicle is at rest and the engine is shut off. The parking lock hereby blocks—as a result of a corresponding actuation by the driver—the driven transmission shaft which is always connected with the drive wheels so as to be secured against rotation, at least by bringing a pawl arranged in the automatic transmission into engagement with the toothing of a parking lock wheel arranged on the driven transmission shaft.
In principle, various mechanical, electrohydraulic and electromechanical systems are known as a transmission device between such parking lock constructed, for example, as a pawl and the actuating device for the vehicle transmission arranged in the passenger compartment of the automobile. Mechanical transmission devices for actuating the parking lock include, for example, a Bowden cable between the selection lever located in the passenger compartment and the transmission control arranged on the automatic transmission.
To improve the structural design with respect to the free arrangement of the actuating device in the passenger compartment, and to ensure an improved acoustic decoupling of the actuating device from the drive train of the automobile, modern automobiles or automatic transmissions increasingly employ a shift-by-wire principle, because modern automatic transmission are increasingly controlled entirely electronically.
Such “shift-by-wire” transmissions transmit the shift commands from the actuating device or from the selection lever of the automatic transmission generally exclusively electrically or electronically. In some situations, the parking lock may even be actuated automatically, for example with “Auto-P”, where the parking lock is automatically engaged when the ignition key is pulled out or the occupants exit the automobile.
However, there is the additional requirement that the parking lock must also be operable mechanically when electronic systems fail or the electrical power supply of the automobile fails, so that the vehicle can be moved even under these circumstances. This may occur, for example, when the vehicle is in a repair shop or is towed in the event of a defect. Shift-by-wire actuating devices for automatic transition are known, where an additional mechanical connection, for example a Bowden cable, is installed between the selection lever and the transmission. The parking lock can then be operated mechanically by way of the Bowden cable even if the electrical systems fail completely, so that the vehicle can always be moved and again safely be parked.
To minimize the actuating travel of the Bowden cable between the actuating device and the transmission, to prevent unnecessary wear of the mechanical parking lock actuator and to minimize drag caused by the mechanical parking actuation when the selection lever is operated, actuating devices have been developed where the Bowden cable for the mechanical actuation of the parking lock can be selectively moved only when the selection lever is actually shifted into or out of the parking lock position. Conversely, the mechanical parking lock actuation is decoupled from the selection lever during all other movements of the selection lever between the individual gear stages or shift gates—by a corresponding design of the mechanical transmission linkage in the actuating device. The other selection lever movements can then be easily performed, without feedback of the friction forces from the mechanical parking lock actuation to the selection lever.
An actuating device of this generic type is disclosed, for example, in the patent DE 103 26 118 B4. This conventional actuating device includes a selection lever movable along a shift gate and a Bowden cable as a mechanical transmission means for actuating the parking lock. This conventional actuating device also includes a mechanical transmission linkage with a multiple joint linkage in form of coupled transmission elements, wherein the multiple joint linkage operates the Bowden cable to the parking lock—only when the selection lever is moved into the parking lock position or out of the parking lock position.
However, the design and installation of this conventional actuating device is relatively complex, in particular due to the multiple joint linkage in this actuating device which has a plurality of fork-shaped transmission elements that must be brought into engagement with a control plate arranged on the selection lever. Moreover, the conventional actuating device is initially limited to a movement of the selection lever along only a single shift gate, because the selection lever cannot be tilted to the side as a result of the multiple joint linkage formed at that location.
In order to be able to use this conventional actuating device also in conjunction with selection levers to be moved along several shift gates, for example in an automatic shift gate and in a manual touch gate, either the entire arrangement formed of selection lever, control plate and multiple joint linkage must be expanded by an additional universal joint and pivotally supported, or an additional swivel joint must be provided in the shaft of the selection lever. This conventional actuating device may also exhibit rattling noises when the components of the employed multiple link connection do not engage with each other and with the control plate completely without play.
Actuating devices also known in practice where the selective mechanical transmission linkage between the selection lever and the Bowden cable is implemented in form of a plurality of sequentially connected sliders or transmission elements with up to five interposed contact surfaces or transitions between components, in order to thereby solve the problem of sideways movement of the selection lever while simultaneously selectively transmitting the force to the Bowden cable. However, the corresponding component tolerances of the sequentially arranged transmission elements or the corresponding play between the adjoining transmission elements are additive, requiring the components in those actuating devices to be manufactured and installed with particularly exact tolerances.
In view of this background, it is an object of the present invention to provide an actuating device, with which the installation of the mechanical transmission linkage for selective actuation of the transmission means to the parking lock can be simplified, while simultaneously ensuring a smooth, reliable and low-noise actuation. Another important object of the present invention is to construct the mechanical transmission linkage so as to be suitable for actuating devices having more than one shift gate. Moreover, potential cost savings compared to known conventional solutions with more complex structures will be described.